This invention relates generally to a rotary device or unit, and more particularly, to an improved rotary device having means facilitating an increased power shaft diameter.
Rotary expansion engines or power units of the type having a housing defining an epitrochoidal cavity, a planetating rotor element movable within such cavity and an eccentric or lobe means integrally formed with the power shaft on which the rotor rotates are well known in the art. It is also well known that the expansion force in these rotary expansion devices can be provided either by pressured expansion fluid or by internal combustion means and that certain of these expansion devices, particularly the devices utilizing pressurized expansion fluid, can also function equally well as a compression device, such as an air compressor. Thus, although the description of the present invention is directed primarily to a rotary expansion device utilizing pressurized expansion fluid, it is understood that the inventive principles apply to rotary expansion devices utilizing internal combustion means and rotary compression devices as well. In the conventional rotary device, the rotation of the rotor about the eccentric or lobe portion and the revolution of the radial center of the rotor about the center line of the power shaft are controlled by what are known in the art as phasing gears. These phasing gears include an internal ring gear formed within, and rotatable with, a portion of the rotor and an external pinion or stationary gear fixed with respect to the device housing. As a result of engagement between the ring and pinion gears, the rotor is caused to rotate about the eccentric or lobe portion during its revolution about the axis of the power shaft. The relationship between the ring and pinion gears is such as to insure continuous contact between each of the apices of the rotor element and the inner wall of the epitrochoidal cavity. These rotary engines or power units also include appropriate seals and valving means for selectively directing expansion fluid, in the case of a rotary expansion device utilizing this type of expansion force into the plurality of expansion chambers defined by the engine housing and the outer surfaces of the rotor. A typical rotary expansion unit of this type is described in Hoffmann U.S. Pat. No. 4,047,856.
Rotary devices or units have several design variables. One such variable is the number of lobes in the epitrochoidal cavity, and thus the number of apices on the rotor. A rotary device or unit of common construction is one having an epitrochoidal cavity with two opposing lobes and a planetating rotor with three apices. This is the type of unit described and illustrated in U.S. Pat. No. 4,047,856. In rotary expansion engines of this type, it is axiomatic that the ratio between the internal ring gear in the rotor and the external stationary or pinion gear fixed to the housing must be 3:2. In other words, the pitch diameter of the ring gear must be one and one half times greater than the pitch diameter of the pinion gear. Accordingly, the internal ring gear has one and one half times as many teeth as the external pinion gear. A further relationship necessary in this type of unit is that the pitch diameter of the internal ring gear must be exactly six times the rotor eccentricity, which is the distance between the axial center line of the power shaft and the axial center line of the rotor, and the pitch diameter of the pinion gear must be exactly four times this same eccentricity. Thus, the sizes of the ring gear and pinion gear for a given eccentricity are specified and thus limited. Because one end of the power shaft must pass through the center of this pinion gear, the diameter of such shaft is also necessarily limited. Clearly, it can be no greater than the pitch diameter of the pinion gear less the necessary radial material needed to support the gear teeth. In a conventional rotary unit as described above having a two lobe epitrochoidal cavity, the pitch diameter of the pinion gear is four times the eccentricity. In a rotary device characterized by an "inner envelope" shaped rotor, an epitrochoidal cavity having M lobes will have a rotor with M+1 faces or apices. In the specific case of Hoffmann U.S. Pat. No. 4,047,856, M=2, thus M+1=3. It thus follows that in the general case, the fixed pinion gear in an "inner envelope" shaped rotor will always be related to the ring gear in the ratio of M/(M+1) with respect to the tooth ratio and the pitch diameters.
The limitation of power shaft diameter resulting from the heretofore necessary relationship between the pitch diameters of the ring and pinion gears and the eccentricity leads to several disadvantages or limitations of conventional rotary units. First, the power shaft is limited to how much torque it can carry. Secondly, the power shaft is known to bend due to the radial forces imposed on the rotor, thus imposing undesirable vibrations on the mechanism. Thirdly, the bending of the power shaft as mentioned above sometimes causes the pinion gear to break and may cause wear in the pinion gear bearing of a "bell mouth" pattern. Fourthly, the conventional power shaft results in a journal bearing which may be of inadequate area to carry the load imposed by the rotor.
Because of the above limitations, there is a need in the art for a rotary expansion or compression device capable of facilitating a power shaft with an increased diameter which has heretofore been limited because of design constraints dictated by the relationships between ring and pinion gear pitch diameters and rotor eccentricity.